With a one-input-one-output workflow, as supported by the prior art, color management was not typically required. Images were typically scanned by a professional operator using a single scanner producing a color representation, e.g., cyan, magenta, yellow, and black (CMYK) format, that was tuned to a single output device. Spot colors were handled either by mixing spot inks or by using standard CMYK formulas in swatch books. An accurate monitor display was not typically available. The system worked because the CMYK values that the scanner produced were tuned for the output device, forming a closed loop that dealt with one set of numbers.
More recently, the types of input and output devices have increased dramatically. Input devices include not only high-end drum scanners but also high-end flatbed scanners, desktop flatbeds, desktop slide scanners, and digital cameras. Output devices include not only web and sheetfeed presses with waterless inks, soy inks, direct-to-plate printing, and Hi-Fi color but also digital proofers, flexography, film recorders, silk screeners, color copiers, laser printers, inkjet printers, and even monitors that function as final output devices. The diversity of input and output devices vastly complicates the approach of a closed workflow as previously discussed. Thus, possible workflows may be associated with a many-to-many mapping of input devices to output devices.
The result is a potentially huge number of possible conversions from input devices to output devices. With an m-input to n-output workflow, one may need m×n different conversions from the input to the output. With the increasing diversity of input and output devices, the task of providing desired color conversions from input to output can easily become unmanageable.
Color management is a solution for managing the different workflows that may be supported between different input device and output device combinations. Color management typically supports an intermediate representation of the desired colors. The intermediate representation is commonly referred as a profile connection space (PCS), which may be alternately referred as a working space. The function of the profile connection space is to serve as a hub for the plurality of device-to-device transformations. With such an approach, the m×n link problem is reduced to m+n links, in which only one link is needed for each device. Each link effectively describes the color reproduction behavior of a device. A link is commonly referred as a device profile. A device profile and the profile connection space are two of the four key components in a color management system.
As based upon current International Color Consortium (ICC) specifications, the four basic components of a color management system are a profile connection space, a set of profiles, a color management module (CMM), and rendering intents. The profile connection space allows the color management system to give a color an unambiguous numerical value in CIE XYZ or CIE LAB color space that does not depend on the quirks of the plurality of devices being used to reproduce the color but instead defines the color as a person actually sees the color. (Both CIE XYZ and CIE LAB are color spaces that are modeled as being device independent.) A profile describes the relationship between a device's RGB (red, green, and blue) or CMYK control signals and the actual colors that the control signals produce. Specifically, a profile defines the CIE XYZ or CIE LAB values that correspond to a given set of RGB or CMYK numbers. A color management module (CMM) is often called the engine of the color management system. The color management module is a piece of software that performs all of the calculations needed to convert the RGB or CMYK values. The color management module works with the color data that is contained in the profiles. Rendering intents includes four different rendering intents. Each type of rendering intent is a different way of dealing with “out-of-gamut” colors, where the output device is not physically capable of reproducing the color that is present in the source space.
As a workflow becomes more complex, color management becomes more important to the user for managing colors of an image file as the image file flows from input (e.g., a scanner) to output (e.g., printer). A workflow utilizes four stages of color management that include defining color meaning, normalizing color, converting color, and proofing. Defining the color meaning includes determining if a profile is embedded in the content and defining a profile if there is no embedded profile. The workflow can then proceed with normalizing color to a working space (corresponding to a device independent color space) or with converting the color representation of the image file directly to the destination space. If the color is normalized to a working space, operations are performed in the working space, e.g., the user modifying selected colors in the working space. A color management system can then determine a transformation table from the source profile and the destination profile, using the common values from the working space. Consequently the color management system can convert a source image to a destination image using the transformation table.
With the prior art, color management is typically administered at both the application level and the device level. For example, with the Adobe® Photoshop® software application, which is a professional image-editing standard for producing high quality images for print and the Web, the user configures the application in accordance with a policy. The policy is a set of rules or actions that may be dependent on different contingencies. For example, with an untagged document, the Photoshop application can assume a profile, assign a profile, or assign a profile and do a conversion to some other profile in accordance with user selections selected by the user in a dialog box. The user typically responds to a plurality of dialog boxes in order to establish the desired policy. The Photoshop application allows the user to configure other aspects of color management, including configuring printer controls (e.g., a printer profile and rendering intent). If, however, the output device is changed, the user typically must re-enter the appropriate dialog and modify the policy.
The above example illustrates a common deficiency with the prior art. In particular, a policy is established for each combination of application, device, and system. A user may use a plurality of applications in processing colors documents, where each application requires the user to respond to a series of dialog boxes for each application. Moreover, the user may process a color document from one of a plurality of input devices and to one of a plurality of output devices with one or more applications. Furthermore, in a commercial or educational setting a plurality of users may use the same system or each of a plurality of users may use a different system in which the consistency of color management policies is desired. Having to configure policies separately for each application, device, user, and system can be very demanding on the user. Hence, there is a real need in the industry to provide a more integrated and consolidated approach for controlling the policies of color management systems.